Due to costs and time requirements, it is desirable to minimize and selectively perform maintenance at intervals where the likely benefits outweigh the costs. At the same time, it is desirable to minimize the risks of performing maintenance too infrequently, particularly for mission critical applications. Therefore, a preventative maintenance approach is often adopted to regularly inspect components. However, scheduled preventive maintenance actions can undesirably increase costs, both in terms of labor and parts, while also undesirably preventing the use of the component being maintained.
Condition-based maintenance (or monitoring) (CBM) is a concept developed to reduce costs associated with preventative maintenance, where maintenance is ideally performed only on an as-needed basis in response to an indication of potential deterioration or degradation. However, practical implementation of CBM and prognostics health management (PHM) for many applications is difficult due to real-world uncertainties and complexities. For example, in the case of aircraft, a structural component may have a complex geometry, be riveted or interconnected with other structural components, and be subjected to varying and unpredictable loading. While various approaches have been developed to estimate remaining usage life (RUL), they generally tend to be overly simplistic and not extensible to complex structures, too conservative resulting in excess maintenance, or impractical for real-time prognostics applications, while also often failing to account for all potential sources of uncertainty.